1. Field of the invention.
The present invention relates to a pump for inflating an inflatable member, and more particularly to hand pumps.
2. Description of the prior art.
A various assortment of hand pumps have been proposed for use in inflating an inflatable member, such as a tire. Particularly when utilized to inflate a tire, such pumps are normally provided with a hose having an attachment at its outer end which is threaded onto a valve stem of the tire. Since tires have a recommended pressure at which they should be used, it is desirable to known the pressure in the tires as the pumping proceeds. Anyone who has inflated a tire with a hand pump is aware of the difficulty and inconvenience involved in obtaining the correct pressure in the inflated tire. First, the tire is inflated to an estimated pressure, after which the hose attachment is unthreaded from the valve stem, and the pressure must then be checked with a separate pressure gauge. If the pressure in the tire is insufficient, the hose is reattached to the stem, and the tire is inflated an additional amount, after which the hose is removed and the pressure is again checked with the gauge. This procedure may continue a number of times until the desired pressure is attained, during which the hose may be attached and removed a number of times to verify the pressure in the tire.
If the tire has been overinflated, a pin in the valve stem must be depressed or removed to deflate the tire somewhat, after which the pressure in the tire is again checked. If deflation of the tire is insufficient, an additional amount of air must be removed from the tire until the correct pressure is obtained. Thus, both inflation and deflation of the tire is attended by a considerable amount of inconvenience resulting from multiple attachments and removals of the hose, due to the necessity of removing the hose when the pressure is checked with a gauge and when the tire is deflated.
In addition, if the tire must be inflated at a user's home or "on the road" in an emergency situation, a pressure gauge may be unavailable. In such a case, the tire must be inflated to an estimated pressure which may be quite different from the recommended amount, and damage may result to the tire during its subsequent use.
A double-acting pump is disclosed in Wickenberg et all. U.S. Pat. No. 3,485,180.